Tn = a + a+d + a+2d .... + a +(n-1) d
T3 = a +2d
T8 = a + 7 d
so
a + 2d = 2 (a+7d)
a + 2d = 2 a + 14 d
a + 12 d = 0
a = -12 d
sum of first 25 = (n/2)[ 2a +(n-1)d ]
= (25/2) [ -24 d + (24) d ]
LOL !!!
= 0
In an arithmetic series the 3rd term is twice the 8th term. Find the sum of the first 25 terms.
2 answers
oo hanks i am doing this sum form hours to hours .ur great
1 answer